Brazed bicycle frame and method for making

ABSTRACT

A brazed bicycle frame and method for making. At least two bicycle frame half-shells are fabricated. A filler metal is then placed between the bicycle frame half-shells to form a two-part hollow frame section. The two-part hollow frame section is inserted into a hot volume at a temperature higher than the melting temperature of the filler metal but lower than the melting temperature of the two bicycle frame half-shells. The filler metal is allowed to melt. The filler metal is then allowed to cool and harden to form a rigid joint. In one preferred embodiment the bicycle frame half-shells each have a flange that facilitates alignment fixturing and assembly of the two-part hollow frame sections. In another preferred embodiment the filler metal and the bicycle frame half-shells are placed in an extruded or formed grooved section. The grooved section also facilitates alignment fixturing and assembly of the two part hollow frame sections, and helps to strengthen the braze joint.

[0001] This invention relates to bicycles, and more specifically tobicycle frames. This application is a continuation-in-part of Ser. No.09/431,878 filed Nov. 2, 1999, which is a continuation-in-part of U.SPat. No. 5,975,550.

BACKGROUND OF THE INVENTION

[0002] The history of the bicycle goes back many years. A crudetwo-wheeled vehicle propelled by the feet was popular as early as thesecond half of the 17^(th) century. Extensive developments to the designof the bicycle were made during the 19^(th) century. At the end of the19^(th) century, the bicycle had become a serious means oftransportation. In 1899, the U.S. production of about 1,000,000 bicyclesa year was valued at $31,000,000. However, by 1909 the bicycle industryin the U.S. was nearly nonexistent due to the advent of the motorcycleand automobile. Bicycle riding was generally confined to children and tosmall groups of devotees, such as members of the League of AmericanWheelmen, organized in 1880 and the Century Road Club Association,organized in 1899.

[0003] It was not until the 1960's and 1970's and more recently in the1990's that bicycling once again began to enjoy strong popularity. Thereare several modem reasons that may have resulted in this strongresurgence. Air pollution, traffic congestion, and the high cost ofautomobile fuel are all reasons that it makes sense to use a bicycle fortransportation. Personal fitness is also a modem trend that is verypopular. The bicycle is an outstanding device to use for physicalexercise.

[0004] As the bicycle has developed and has become firmly established aspart of our modem culture, its use has expanded in recent years. Forexample, in addition to the traditional road bicycle, mountain bikes andBMX bikes are now very popular.

Bicycle Frames

[0005] As bicycle frame technology has improved, bicycle designers havefocused on making bicycle frames that are lightweight and strong.Similarly, bicycle designers are concerned about building bicycle framesin a cost effective and time efficient manner. Monocoque bicycle framesare extremely popular for road, mountain, and BMX bicycles. A monocoquestructure is one in which the skin absorbs all or most of the stressesto which the structure is subjected.

[0006] There are two common methods for making a hollow monocoquebicycle frame. The first method is by extruding individual hollowtubular frame sections. These frame sections can then be cut to length,bent to a desired shape, coped, aligned and then individually weldedtogether to produce a bicycle frame. Some of the major disadvantages tomaking bicycle frames in this manner are: 1) the manufacturer is limitedby available extruded tubing material and sizes, 2) the thickness andcross section of the tube cannot vary with stress, 3) the amount andtype of bending and coping that he is able to do to the extruded framesections, and 4) the extra time it takes to individually align and weldeach frame member together, and 5) the time necessary to align eachframe after welding.

[0007] The second known method involves forming matching framehalf-shells and then welding them together along their entire seam. Theadvantage of the second method over the first is that the crosssectional area of the welded frame sections can vary along their length.However, welding formed matching half-shells along their entire seam isa time consuming and complicated process. Because welding a bicycleframe is considered to be delicate work, welders have to be highlytrained or high cost robotic welders are used to do an effective,consistent and esthetically acceptable job. Therefore, it is much moreexpensive to weld formed matching half-shells together than it is toextrude individual frame sections and then weld those together.

Brazing

[0008] Brazing is a method of joining together metals by inserting theentire work into a hot volume (such as a molten salt bath or a hotfurnace) and using a filler metal with a melting point lower than thatof the metals to be joined. Brazing is well known in the prior art.

[0009] What is needed is a more efficient method for making monocoquebicycle frames.

SUMMARY OF THE INVENTION

[0010] The present invention provides a brazed bicycle frame and methodfor making. At least two bicycle frame half-shells are fabricated. Afiller metal is then placed between the bicycle frame half-shells toform a two-part hollow frame section. The two-part hollow frame sectionis inserted into a hot volume at a temperature higher than the meltingtemperature of the filler metal but lower than the melting temperatureof the two bicycle frame half-shells. The filler metal is allowed tomelt. The filler metal is then allowed to cool and harden to form arigid joint. In one preferred embodiment the bicycle frame half-shellseach have a flange that facilitates alignment fixturing and assembly ofthe two-part hollow frame sections. In another preferred embodiment thefiller metal and the bicycle frame half-shells are placed in an extrudedor formed grooved section. The grooved section also facilitatesalignment fixturing and assembly of the two part hollow frame sections,and helps to strengthens the braze joint.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 shows a bicycle frame in which the rear portion of theframe has been brazed.

[0012]FIG. 2 shows an upper frame half-shell and a lower framehalf-shell and filler metal.

[0013]FIG. 3 shows the components shown in FIG. 2 brazed together.

[0014] FIGS. 4A-4D show a procedure for making a preferred embodiment ofthe present invention.

[0015]FIG. 5 shows another preferred embodiment of the presentinvention.

[0016]FIG. 6 shows another preferred embodiment of the presentinvention.

[0017] FIGS. 7 - 14 show a procedure for making another preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Preferred embodiments of the present invention can be describedby reference to FIGS. 1-14.

Brazing a Bicycle Frame

[0019]FIG. 1 shows a side view of a first preferred embodiment of thepresent invention in which chain stay 2 and seat stay 4 of rear portion6 of bicycle frame 8 have been brazed. FIG. 2 shows a detailed view ofthe components of seat stay 4 prior to it being brazed. To braze seatstay 4, upper frame half-shell 9 and lower frame half-shell 10 are firstcleaned. Then, braze filler metal 11 is placed between upper framehalf-shell 9 and lower frame half-shell 10 and the two halves areassembled. In a preferred embodiment, the upper and lower framehalf-shells are aluminum alloy and filler metal 9 is an aluminum brazingalloy. Connecting pins 12 help align and assemble upper frame half-shell9 appropriately with lower frame half-shell 10. After the two halves areassembled, seat stay 4 appears as shown in FIG. 3. Seat stay 4 is theninserted into a heated volume at approximately 1,400 degrees Fahrenheitto melt the aluminum alloy braze filler metal 11. In a preferredembodiment the heated volume is a molten salt bath. Seat stay 4 is thenremoved from the molten salt bath and it cools. Consequently, fillermetal 11 re-hardens, brazing together upper frame half-shell 9 and lowerframe half-shell 10.

[0020] Similarly, the front portion of bicycle frame 8 can also bebrazed from two halves. By referring to FIG. 2, the advantages ofbrazing are made very clear. The manufacturer is able to preciselymachine upper frame half-shell 9 and lower frame half-shell 10 to theexact shape and thickness he needs for the bicycle frame section. Also,many frame sections and joints can be simultaneously and uniformlybrazed at once in the same heated volume, saving time and money in theconstruction process. Furthermore brazing uniformly heats the framesections minimizing distortion and eliminating the need for alignmentafter brazing.

Grooved Brazing Method

[0021] A second preferred embodiment is shown in FIGS. 4A-4D. As shownin FIG. 4A, grooved section 15 is aligned with upper frame half-shell 17and lower frame half-shell 16. A preferred grooved section 15 is shownin FIG. 4D. In the second preferred embodiment, grooved section 15 isextruded 6061 aluminum and is approximately ¼ inch in diameter. Grooves24A and 24B are rectangular and have a width of approximately 0.07 inch.Upper frame half-shell 17 and lower frame half-shell 16 are alsopreferably 6061 aluminum and are approximately 0.063 inch thick. Asshown in FIG. 4A, the cross section of grooved section 15 is in thegeneral shape of an H-section. Braze filler metal 19 is placed ingrooves 24A and 24B. Braze filler metal 19 is preferably an aluminumbrazing alloy. Upper frame half-shell 17 and lower frame half-shell 16are then assembled together by inserting them into grooves 24A and 24Bin grooved section 15 to form joined frame section 20, as shown in FIG.4B. Grooved sections 15 holds upper frame half-shell 17 and lower framehalf-shell 16 in assembled alignment as shown in FIGS. 4B and 4C. Notethat in FIG. 4C, upper frame half-shell 17 and lower frame half-shell 16bend at bend 18. Grooved section 15 is pliable and therefore it can bebent so that it adjusts easily to the shape of the upper and lowerhalves.

[0022] The second preferred embodiment provides a significant timesavings because grooved section 15 automatically aligns upper framehalf-shell 17 so that it is positioned directly above lower framehalf-shell 16. In the second preferred embodiment, prior to applyingheat to frame section 20, upper frame half-shell 17 and lower framehalf-shell 16 are secured together to ensure that their desired matingrelationship does not alter during the brazing process. A preferredmethod of securing them together is with the use of clamps. Then, upperframe half-shell 17 and lower frame half-shell 16 are heated and arebrazed together in a manner similar to that described in the firstpreferred embodiment.

[0023] Although FIGS. 4A-4C show grooved section 15 resembling anH-section in which the grooves are directly opposite one another, it isalso possible to adjust the grooves so that they are at other angles.FIG. 5 shows grooved section 21 where the upper groove is angled to theleft of the lower groove. FIG. 6 shows grooved section 22 in which thegrooves are at 90 degrees to one another.

Flanged Half-Shell Brazing Method

[0024] A third preferred embodiment is shown in FIGS. 7-14.

Forming Flanged Half-Shells

[0025] In the third preferred embodiment, a flat section of any brazablesheet metal 30 (such as aluminum, stainless steel, or titanium) isformed into a half shell by mold 31. In the preferred embodiment, sheetmetal 30 is 6061 aluminum and is approximately 0.050 inch thick. Formingpressure is imparted to the top of sheet metal 30 causing it to assumethe shape of mold 31 and become upper frame half-shell 32, as shown inFIG. 8. If necessary, excess aluminum is cut away, leaving flange 35around upper frame half-shell 32. Preferably, flange 35 extendsapproximately {fraction (3/4)} inch out from the outside edge of upperframe half-shell 32 to allow for clamping or the creation of otheralignment, fixturing or assembly features. In a similar fashion amatching lower frame half-shell 34 is formed (FIG. 10).

Assembling then Brazing the Flanged Half-Shells

[0026] As shown in FIG. 10, upper frame half-shell 32 is aligned andassembled to lower frame half-shell 34. Braze filler metal 36 is placedbetween upper frame half-shell 32 and lower frame half-shell 34. FIG. 11shows a front view of upper frame half-shell 32 secured together withclamps 37 to lower frame half-shell 34 with braze filler metal 36inbetween. In a preferred embodiment, braze filler metal 36 is pastedbetween upper frame half-shell 32 and lower frame half-shell 34. Clamps37 are then tightened and upper frame half-shell 32 and lower framehalf-shell 34 are heated and brazed together in a manner similar to thatdescribed in the first preferred embodiment.

Removing the Flange

[0027] After upper frame half-shell 32 and lower frame half-shell 34have been heated and filler metal 36 has hardened, clamps 37 areremoved, as shown in FIG. 12. Trimming tool 38, such as a router or endmill, is then run along the seam of the brazed two-part hollow framesection and flanges 35 are cut away. FIG. 13 shows a front view and FIG.14 shows a perspective view of upper frame half-shell 32 brazed to lowerframe half-shell 34 after flanges 35 have been trimmed away.

[0028] Of the three preferred embodiments discussed above, Applicantsestimate that the third preferred embodiment provides the lowest costbicycle frame manufacturing method. The same forming, brazing andtrimming tools and procedures can be used for different sheet metaltypes (such as, titanium, aluminum, or stainless steel). Also, not onlydoes the flange function as a temporary alignment, assembly andfixturing area, it further functions as a temporary placement area forthe braze filler metal. For example, when the two part frame section isheated during the brazing process the flanges are able to contain themelted braze filler metal so that any excess melted braze filler metalis prevented from flowing onto the outer formed surfaces of the two partframe section.

[0029] While the above description contains many specifications, thereader should not construe these as limitations on the scope of theinvention, but merely as exemplifications of preferred embodimentsthereof. Those skilled in the art will envision many other possiblevariations are within its scope. For example, although it was statedthat in the second preferred embodiment that upper frame half-shell 17and lower frame half-shell 16 are clamped together to ensure that theirdesired mating relationship does not alter during the brazing process,it would also be possible to braze upper frame half-shell 17 and lowerframe half-shell 16 together without using a separate clamping device.Friction provided by grooved section 15 would properly hold upper framehalf-shell 17 and lower frame half-shell 16 in their proper matingrelationship during brazing. Although FIG. 7 shows sheet metal 30 beingformed by mold 31, it is also possible to form flanged half-shells bymachining them. However, the cost is much greater. Also, although FIG.11 shows upper frame half-shell 32 and lower frame half-shell 34 clampedtogether, it would also be possible to crimp the flanges together. Or,the flanges could be held together with tabs. Or, the flanges could havemating holes and studs and the flanges could be snapped together.Although, FIG. 11 shows braze filler metal 36 pasted between upper framehalf-shell 32 and lower frame half-shell 34, this process could besimplified by the use of a brazing sheet whereby the braze filler metalsheet is roll bonded to the base metal sheet, thereby eliminating theneed for a separate time consuming step of pasting filler metal betweenthe half-shells. An advantage of the above preferred embodiments isfound in the fact that at the junction between the upper framehalf-shell and the lower frame half-shell there is a smooth seam. Thiscontrasts with welding, which by nature of the process produces a seamthat has a rippled appearance. As shown in FIG. 15, it is possible tofurther trim the seam of the brazed two-part hollow frame section tohave a seam that is at the same level as upper frame half-shell 32 andlower frame half-shell 34 so that it will be virtually invisible afterpainting the hollow frame section. Also, although the above embodimentsdiscussed how to braze the upper frame half-section to the lower framehalf-section by melting a filler metal after the upper framehalf-section and the lower frame half-section are inserted into a hotvolume, it is also possible to braze the upper frame half-section andthe lower frame half-section together my melting the filler metal with ahand held torch. Disadvantages associated with torch brazing framehalf-sections together are similar to the disadvantages associated withwelding the frame half-sections together. For example, like welding,torch brazing formed matching half-shells along their entire seam is atime consuming and complicated process. It is considered to be delicatework, therefore torch brazers have to be highly trained or high costrobotic torch brazers are used to do an effective, consistent andesthetically acceptable job. Also, although the above preferredembodiments for brazing were discussed in relation to a bicycle frame,the above procedures could also be applied when building other types ofmonocoque structures. For example, these procedures could be used forbuilding airplane wing sections or the hull or mast of a sailboat.Accordingly the reader is requested to determine the scope of theinvention by the appended claims and their legal equivalents, and not bythe examples which have been given.

I claim:
 1. A process for making a hollow bicycle frame sectionutilizing brazing, comprising the steps of: A) fabricating at least twobicycle frame half-shells, B) placing a filler metal between said atleast two bicycle frame half-shells to form a two-part hollow framesection, C) inserting said two-part hollow frame section into a hotvolume at a temperature higher than the melting temperature of saidfiller metal but lower than the melting temperature of said at least twobicycle frame half-shells, and D) allowing said filler metal to melt,and E) allowing said filler metal to cool and harden to form a rigidjoint to form said hollow bicycle frame section.
 2. The process as inclaim 1 , further comprising the step of securing together said at leasttwo bicycle frame half-shells prior to inserting said two-part hollowframe section into said hot volume.
 3. The process as in claim 1 ,wherein said step of placing a filler metal between said at least twobicycle frame half-shells to form a two-part hollow frame section isachieved by the following sub-steps: A) fabricating a grooved sectioncomprising at least two grooves, and B) inserting said filler metal andsaid at least two bicycle frame half-shells in said at least twogrooves.
 4. The process as in claim 3 , wherein said grooved section isfabricated by extrusion.
 5. The process as in claim 3 , wherein saidgrooved section is fabricated by forming.
 6. The process as in claim 3 ,wherein said at least two grooves are separated by an angle ofapproximately 180 degrees.
 7. The process as in claim 3 wherein said atleast two grooves are separated by an angle less than approximately 180degrees.
 8. The process as in claim 1 , wherein said at least twobicycle frame half-shells each comprise at least one flange.
 9. Theprocess as in claim 8 , wherein said two-part hollow frame section isassembled by aligning and securing together said flanges of said atleast two bicycle frame half-shells.
 10. The process as in claim 8 ,wherein said flange removed after brazing.
 11. The process as in claim 1, wherein said hollow bicycle frame section is a chain stay section. 12.The process as in claim 1 , wherein said hollow bicycle frame section isa seat stay section.
 13. The process as in claim 1 , wherein said hollowbicycle frame section is a front triangle section.
 14. A brazed hollowbicycle frame section comprising: A) at least two bicycle framehalf-shells, and B) a filler metal located between said at least twobicycle frame half-shells and joining them to form a two-part hollowframe section, wherein said hollow bicycle frame section is produced bybrazing.
 15. The brazed bicycle frame as in claim 14 , wherein said atleast two bicycle frame half-shells had been clamped together prior toinserting said two-part hollow frame section into a hot volume forbrazing.
 16. The brazed bicycle frame as in claim 14 , furthercomprising a grooved section comprising at least two grooves, whereinsaid filler metal and said at least two bicycle frame half-shells areinserted in said at least two grooves.
 17. The brazed bicycle frame asin claim 16 , wherein said grooved section is an extruded groovesection.
 18. The brazed bicycle frame section as in claim 16 , whereinsaid grooved section is a formed groove section.
 19. The brazed bicycleas in claim 16 , wherein said at least two grooves are separated by anangle of approximately 180 degrees.
 20. The brazed bicycle as in claim16 , wherein said at least two grooves are separated by an angle lessthan approximately 180 degrees.
 21. The brazed bicycle frame as in claim14 , wherein during brazing said at least two bicycle frame half-shellseach comprised at least one flange.
 22. The brazed bicycle frame as inclaim 21 , wherein said two-part hollow frame section is assembled byaligning and securing together said flanges of said at least two bicycleframe half-shells.
 23. The brazed bicycle frame as in claim 14 , whereinsaid hollow bicycle frame section is a chain stay section.
 24. Thebrazed bicycle frame as in claim 14 , wherein said hollow bicycle framesection is a seat stay section.
 25. The brazed bicycle frame as in claim14 , wherein said hollow bicycle frame section is a front trianglesection.